The Austin-Healey 100 itself debuted in 1952 and went into production in 1953 through a partnership between Donald Healey and Austin. The base car used Austin A90 Atlantic mechanicals, producing 90 bhp from a 2,660 cc inline-four engine, and was capable of reaching 100 mph — the source of its name. The standard car was built by Jensen Motors and finished at Austin's Longbridge plant.
To explore the 100's racing potential, five special works development cars carrying "SPL" chassis number prefixes were built between 1953 and 1954. One of these won its class at the 1954 12 Hours of Sebring, prompting the decision to create a limited run of production racing versions. The designation "S" stood for Sebring.
The 100S was built to be as light and as fast as possible. The cast-iron cylinder head of the standard 100 was replaced by an aluminium head designed by Weslake, which combined with other modifications to raise output to 132 bhp at 4,700 rpm. The overdrive unit was deleted to save weight. Dunlop disc brakes were specified on all four corners — a first for any production car worldwide, giving the 100S a significant advantage in braking performance over rivals still relying on drums.
To shed further weight, the 100S deleted bumpers, a convertible hood, and replaced the windscreen with a plastic unit. The grille was reduced in size. These changes produced an overall weight saving of approximately 200 lb (91 kg) compared to the standard car. The aluminium body replaced the standard steel panels. The majority of 100S cars were finished in a two-tone white over Lobelia Blue scheme; a small number were delivered in solid Spruce Green or red, with a single example in black.
The chassis numbering prefix for production cars was "AHS," distinguishing them from the earlier SPL works development cars.
The 100S was raced primarily by private entrants in sports car races across the United States and Europe during 1955 and 1956. Its combination of light weight, strong brakes, and 132 bhp gave it genuine competitiveness in its class.
One of the works development SPL cars was campaigned by factory drivers including Lance Macklin, Gordon Wilkins, and Marcel Becquart. This car became associated with one of motorsport's darkest moments: it was involved in the 1955 Le Mans disaster, the crash in which 84 people were killed and 120 injured — the most lethal accident in motor racing history. This particular unrestored works test car sold at Bonhams' December 2011 sale for a world record £843,000.
A separately owned 100S driven by David Shale recorded at least 13 podium finishes, including four outright victories, in British club racing. That car, known colloquially as "EVV," sold at the Bonhams Goodwood Festival of Speed auction on 27 June 2014 for £673,500.
The 100S represents the pinnacle of the original Austin-Healey 100's development and stands as a landmark car in British motorsport history. Its pioneering use of four-wheel disc brakes influenced the wider adoption of the technology in production and competition cars through the late 1950s. The combination of scarcity, racing provenance, and technical significance makes surviving examples among the most sought-after classic British sports cars at auction.
The 100S sits within the broader "Big Healey" family — the three-model line of Austin-Healey 100 and 3000 cars built between 1953 and 1968 — but is distinguished from all other variants by its exclusive construction process, all-aluminium body, and uncompromising focus on competition use.